Effect of anhydrous ammonia treatment on the chemical composition and nutritive value of grass hay and on intake and performance in beef steers

Two compositionally similar, mature grass hays, of dry matter contents 699 and 836 g kg^-1, were treated with anhydrous ammonia at levels of 10, 20 and 30 kg NH₃ t DM^-1 and 20, 30 and 40 kg NH₃1 DM^-1, respectively. Treatment at 10 kg t^-1 did not inhibit moulding of the damp hay. The remaining treatments increased the nitrogen contents of damp and dry hay, respectively, from 12.5 and 13.8 g kg DM^-1 to maxima of 250 and 270 g kg DM^-1 and the water-soluble ammonia-nitrogen contents of oven-dried samples from 24 and 23 g kg^-1 to maxima of 118 and 88 g kg^-1 of total nitrogen. While all treated hays had reduced levels of insoluble hemicellulose, ammoniation increased the insoluble cellulose content of damp hay only. In trials of 37 and 80 days duration, respectively, the untreated and 20 and 30 kg t^-1‘damp'-ammoniated hays and the untreated and 20, 30 and 40 kg t^-1‘dry'-ammoniated hays were offered ad libitum, unsupplemented or supplemented with 2 kg d^-1 of a barley-soya compound, to steers of 328 kg and 383 kg mean initial liveweight. Steers offered untreated and 20 and 30 kg t^-1 ammoniated damp hays and untreated and 20, 30 and 40 kg t^-1 ammoniated dry hays, all ad libitum and alone, consumed 5.50, 6.48 and 6.59 and 6.78, 782, 790 and 8.26 kg d^-1 and gained 471,560 and 521 g d^-1 and 490,699,794 and 572 g d^-1, respectively. When supplemented, the same hays, again offered ad libitum, produced live-weight gains of 529, 515 and 736 g d^-1 and 725, 705,726 and 895 g d^-1, respectively. The apparent in vivo digestibilities of hay dry matter, organic matter, gross energy, hemiceliulose, cellulose and nitrogen were significantly increased by ammoniation.